Optimal EMG signal bandwidth and interelectrode distance for the recording of acoustic, electrocutaneous, and photic blink reflexes

The bandwidth for the recording of the orbicularis oculi blink reflex electromyogram (EMG) response is optimal when low-frequency artifacts, such as motion artifacts and cross-talk from other muscles, are maximally suppressed, whereas true EMG signal power is maximally retained. The optimal bandwidth was investigated for acoustic, electrocutaneous, and photic blink reflexes. Reflexes were recorded with varying bandwidth and interelectrode distances of 12 and 36 mm. Power spectra of the EMG signals were calculated and compared with a theoretical spectrum of the uncontaminated EMG signal. For both electrode distances, the optimal bandwidth was on the average 28–500 Hz for acoustic and electrocutaneous blink reflexes and 12–500 Hz for photic blinks. Using photic stimuli, however, a high-pass filter frequency larger than 12 Hz (probably at least 30 Hz) in combination with occlusion of the eye will be necessary to avoid influences of retinal potentials. Given the optimal bandwidth, a larger electrode spacing may be expected to moderately improve the detectability of small blinks in all stimulus conditions.     

Patterns of activity of perioral facial muscles during mastication in man

Summary The activity of buccinator, orbicularis oris superior and inferior, quadratus and triangularis muscles was recorded by surface and needle electrodes during spontaneous unilateral mastication of small or large boluses. Their activity was compared with that of the masticatory muscles masseter and digastric, and with the vertical movement of the jaw. The facial muscles were active during mastication, displaying both tonic and phasic activity. Although the cyclic activity was broadly linked to lowering of the jaw, there was no strict time correspondence between the activity of the various facial muscles themselves, or between the activity of the facial muscles and the digastric. The timing and amplitude of facial muscle activity were affected by the duration of the masticatory cycle, the side on which chewing took place, the size of the bolus, and whether or not lip to lip contact was made.     

Amplitude and bilateral coherency of facial and jaw-elevator EMG activity as an index of effort during a two-choice serial reaction task

In earlier studies, positive but inconsistent relationships have been reported between mental effort and electro-myogram (EMG) amplitude in task-irrelevant limb muscles. In this study, we explored whether facial EMG activity would provide more consistent results. Tonic EMG activity of six different facial and jaw-elevator muscles was bilaterally recorded during a two-choice serial reaction task with paced presentation of auditory or visual signals. In Experiment 1, task load (signal presentation rate) was kept constant for 20 min at the level of the subject's maximal capacity. In Experiment 2, task load was increased in a stepwise fashion over six successive 2-min periods from sub- to supramaximal capacity levels. EMG amplitude and coherency between momentary bilateral amplitude fluctuations were measured. In Experiment 1, EMG amplitude of frontalis, corrugator supercilii, and orbicularis oris inferior showed a strong gradual increase throughout the task period, whereas task performance remained fairly stable. Orbicularis oculi, zygomaticus major, and temporalis EMG showed a much smaller increase or no increase. In Experiment 2, the first three muscles showed a fairly consistent increase in EMG amplitude with increasing task load. Orbicularis oculi and zygomaticus major were not active until task load became supramaximal. Effects of stimulus modality or laterality were not found in any experiment. These results are consistent with the notion that EMG amplitude of frontalis, corrugator, and orbicularis oris provides a sensitive index of the degree of exerted mental effort.     

The effect of an active warm-up on surface EMG and muscle performance in healthy humans

The effect of an active warm-up on maximal voluntary contraction (MVC), maximal instantaneous power output and surface EMG (sEMG) parameters was studied. Eight volunteers [mean (SD) 22 (4) years] completed two trials on the same day, one control (CO), and the other preceded by an active cycling warm-up (WU) at 70% ventilatory threshold determined by the ventilatory equivalent method. Quadriceps muscle temperature, measured from vastus lateralis with a flexible thermistor, was 33.8 (0.4)°C in CO compared to 36.8 (0.5)°C in WU (P<0.05). Aural temperature, measured by an infrared tympanic thermistor, was not different between conditions. Experimental trials consisted of three knee-extension maximum voluntary contractions at a 90° angle with simultaneous recording of sEMG from the vastus lateralis, followed by three squat jumps performed on a force platform. SEMGs were analysed in the frequency domain as median frequency (MDF) and in the time domain as root mean square (RMS). MDF was 59.2 (14.1) Hz in CO compared to 67.2 (11.8) Hz in WU (P<0.05), while RMS was higher in CO compared to WU [0.65 (0.28) mV vs. 0.56 (0.19) mV; P<0.05]. MVC was not different [465.7 (107.6) N vs. 490.1 (117.2) N], whilst instantaneous power output during the squat jump was significantly higher in the WU trial [3324 (866) W vs. 3569 (919) W; P<0.05]. These data show MDF to be altered with an active warm-up, which would relate to a greater conduction velocity. This may translate into faster activation of the muscle fibres, thus partly explaining the increase in power output.     

Amplitude and Bandwidth of the Frontalis Surface EMG: Effects of Electrode Parameters

In the present investigation, the frontalis surface EMG was differentially recorded during static voluntary submaximal contractions. First, mean rectified EMG (MREMG) and EMG signal bandwidth were examined for two different bilateral EMG derivations (superior and inferior) with the electrodes placed in horizontal direction and two unilateral derivations (left and right) with the electrodes placed in vertical direction. MREMG was significantly different between the four derivations but absolute differences were small. Bandwidth also varied significantly with derivation. Second, the influence of inter-electrode distance and electrode size was examined for unilateral derivations. The influence of inter-electrode distance on MREMG was significant but the absolute effect was marginal. We suggest that a clear effect is to be expected only within the range of small distances (smaller than 10 mm). The significant effect disappeared when MREMG was expressed as proportion of the MREMG during maximal contraction. This normalization seems to allow better intra-individual or inter-individual comparisons of integrated EMG, especially when different recording methods are used. The influence of inter-electrode distance on bandwidth was not significant. Electrode size had no significant influence on MREMG and bandwidth. EMG power spectra indicated that integrated frontalis EMG can be validly measured only when using recording equipment with a frequency response of 5–500 Hz.     

A simulation model of the surface EMG signal for analysis of muscle activity during the gait cycle

This work describes a model able to synthetize the surface EMG (electromyography) signal acquired from tibialis anterior and gastrocnemious medialis muscles during walking of asymptomatic adult subjects. The model assumes a muscle structure where the volume conductor is represented by multiple layers of anisotropic media. This model originates from analysis of the single fiber action potential characterized by the conduction velocity. The surface EMG of voluntary contraction is calculated by gathering motor unit action potentials estimated by the summation of all activities of muscle fibers assumed to have a uniformly parallel distribution. The parameters related to the gait cycle, such as onset and cessation timings of muscle activation, amplitude of muscle contraction, periods and sequences of motor units' recruitment, are included in the model presented. In addition, the relative positions of the electrodes during gait can also be specified in order to adapt the simulation to the different acquisition settings.     

表面肌电信号的分析与应用

表面肌电信号的检测是一种无创电检测方法 ,它的检测分析对临床诊断及康复医学、运动医学等具有重要意义。本文介绍了表面肌电的信号分析方法 (时域分析法、频域分析法、时频分析法及人工神经网络等方法 ) ,并介绍了表面肌电信号检测分析技术的应用状况和前景展望     

Timing and voluntary suppression of facial mimicry to smiling faces in a Go/NoGo task—An EMG study

Results obtained with a novel emotional Go/NoGo task allowing the investigation of facial mimicry (FM) during the production and inhibition of voluntary smiles are discussed. Healthy participants were asked to smile rapidly to happy faces and maintain a neutral expression to neutral faces, or the reverse. Replicating and extending previous results, happy faces induced FM, as shown by stronger and faster zygomatic activation to happy than neutral faces in Go trials, and a greater number of false alarms to happy faces in NoGo trials. Facial mimicry effects remained present during participants’ active inhibition of facial movement. Latencies of FM were short with 126-250 ms in Go trials, and 251-375 ms in NoGo trials. The utility of the Go/NoGo task, which allows the assessment of response inhibition in the domain of facial expression by installing strong prepotent motor responses via short stimulus presentation times and a great number of Go trials, is discussed.     

Comparison of the EMG power spectrum of the human soleus and gastrocnemius muscles

The purpose of this study was to compare the behaviour of electromyographic (EMG) power spectrum statistics, mean power frequency (MPF) and median frequency (MF), across increasing force levels of the soleus (SO), gastrocnemius medialis (GM) and gastrocnemius lateralis (GL) muscles. Surface EMG signals of these three muscles were recorded in 12 men and 10 women during both (1) ramp (single ongoing contractions with the force increasing linearly from 0 to 100% of the maximum voluntary contraction (MVC); and (2) step (steady force levels: 10, 20, 30, 40, 60 and 80% MVC) static (isometric) plantar flexions. Power spectral analysis of these signals was performed on single 256-ms windows at all of the above-mentioned force levels, for both types of contraction. The MF and MPF were calculated from each of the obtained spectra. A less pronounced increase in the MF or MPF was expected for the SO because of its higher type I fibre content. The main results are as follows: (1) similar behaviours were found in the value of MPF and MF across increasing force for the SO and GL muscles, while the GM gave rise to a different behaviour; (2) no difference was found between ramp and step contractions in the behaviour of either MF or MPF across force levels; and (3) different behaviours were observed between the MF and MPF across increasing force levels, for both ramp and step contractions. Our initial expectations were thus not confirmed. It is concluded that the present results support the hypothesis that the EMG power spectrum may be more sensitive to the diameter of the fibres than to the fibre type proportion of the triceps surae muscles. Furthermore, the sensitivity of the power spectrum statistics of a given muscle to the low-pass filter effect of its skin layer was also emphasized.     

Motor unit activity and surface electromyogram power spectrum during increasing force of contraction

Summary Twelve male subjects were tested to determine the relationship between motor unit (MU) activities and surface electromyogram (EMG) power spectral parameters with contractions increasing linearly from zero to 80% of maximal voluntary contraction (MVC). Intramuscular spike and surface EMG signals recorded simultaneously from biceps brachii were analyzed by means of a computer-aided intramuscular MU spike amplitude-frequency (ISAF) histogram and an EMG frequency power spectral analysis. All measurements were made in triplicate and averaged. Results indicate that there were highly significant increases in surface EMG amplitude (71±31.3 to 505±188 V,p<0.01) and mean power frequency (89±13.3 to 123±23.5 Hz,p<0.01) with increasing force. These changes were accompanied by progressive increases in the firing frequency of MU's initially recruited, and of newly recruited MU's with relatively larger spike ampltitudes. The group data in the ISAF histograms revealed significant increases in mean spike amplitude (412±79 to 972±117 V,p<0.01) and mean firing frequency (17.8±5.4 to 24.7±4.1 Hz,p<0.01). These data suggest that surface EMG spectral analysis can provide a sensitive measure of the relative changes in MU activity during increasing force output.     

Optimal placement of bipolar surface EMG electrodes in the face based on single motor unit analysis

Locations of surface electromyography (sEMG) electrodes in the face are usually chosen on a macro‐anatomical basis. In this study we describe optimal placement of bipolar electrodes based on a novel method and present results for lower facial muscles. We performed high‐density sEMG recordings in 13 healthy participants. Raw sEMG signals were decomposed into motor unit action potentials (MUAPs). We positioned virtual electrode pairs in the interpolated monopolar MUAPs at different positions along muscle fiber direction and calculated the bipolar potentials. Electrode sites were determined where maximal bipolar amplitude was achieved and were validated. Objective guidelines for sEMG electrode placement improve the signal‐to‐noise ratio and may contribute to reduce cross talk, which is particularly important in the face. The method may be regarded as an important basis for improving the validity and reproducibility of sEMG in complex muscle areas.     

Muscle activity and fatigue in the shoulder muscles during repetitive work

Summary The amplitude distribution probability function (ADPF) and the power spectrum of the surface electromyogram from m. deltoideus anterior, m. infraspinatus and m. trapezius pars descendens were analyzed from 7 persons working at a pillar drill. Recordings were performed 6 times during a working day. The ADPF was analyzed from 2–3 work-cycles from each recording. The static contraction level was 11.0% MCV in m. deltoideus anterior, 8.5% MVC in m. infraspinatus, and 20.5% MCV in m. trapezius, without any change occuring throughout the day. When compared to previous suggested upper limits of ADPF levels, both the static and the medium contraction levels were too high in the performance of this particular task. The power spectrum of the EMG was analyzed during isometric contractions of the shoulder muscles. The mean power frequency decreased during the day in m. trapezius only, suggesting muscular fatigue in this area.     

Consequences of prolonged total thermoneutral immersion on muscle performance and EMG activity

We hypothesized that the changes in muscle temperature and interstitial pressure during thermoneutral immersion may affect the reflex adaptation of the motor drive during static contraction, assessed by the decrease in median frequency (MF) of electromyogram (EMG) power spectrum. Ten subjects were totally immerged for 6 h at 35°C and repeated maximal voluntary contraction (MVC) and submaximal (60% MVC) leg extensions sustained until exhaustion. In vastus lateralis (VL) and soleus (SOL) muscles, the compound muscle potential evoked by muscle stimulation with single shocks (M-wave) was recorded at rest, and MF of surface EMG was calculated during 60% MVCs. We measured lactic acid and potassium venous blood concentrations and calculated plasma volume changes. Data were compared to those obtained in the same individuals exercising at 35°C under dry conditions where the MF decrease during 60% MVCs was modest (−4 to−5%). During immersion, the rectal temperature remained stable, but the thigh and calf surface temperatures significantly increased. Lactic acid and potassium concentrations did not vary, but plasma volume decreased from the 180th min of immersion. The M-wave did not vary in VL but was prolonged in SOL from the 30th min of immersion. From the 220th min of immersion, the maximal MF decrease was majored in both muscles (−18 to −22%). Thus, compared to the dry condition, total body thermoneutral immersion enhances fatigue-induced EMG changes in leg muscles, perhaps through the activation of warm-sensitive muscle endings and/or the changes in interstitial pressure because of vasodilatation.     

Influence of motor unit firing statistics on the median frequency of the EMG power spectrum

Summary Changes in the EMG power spectrum during static fatiguing contractions are often attributed to changes in muscle fibre action potential conduction velocity. Mathematical models of the EMG power spectrum, which have been empirically confirmed, predict that under certain conditions a distinct maximum occurs in the low-frequency part of the spectrum, indicating the dominant firing rate of the motor units. The present study investigated the influence of this firing rate peak on the spectral changes during a static fatiguing contraction at 50% of maximum EMG amplitude in the frontalis and corrugator supercilii muscles. An exponential decrease of the median frequency (MF) of the EMG power spectrum was observed when the firing rate peak was absent. When the firing rate peak was present, an exaggerated decrease of MF in the beginning of the contraction was found, which was associated with an increase in firing rate peak magnitude. In later stages of the contraction, a partial recovery of MF occurred, concomitant with a decrease in firing rate peak magnitude.The influence of the firing rate peak on MF was also investigated during nonfatiguing contractions of the frontalis muscle at 20, 40, 60, and 80% of maximum EMG amplitude. A curvilinear relationship between MF and contraction strength was found, whether firing rate peaks were present or absent. The presence of firing rate peaks, however, was associated with a decrease in MF which was inversely related to contraction strength, due to the inverse relationship between firing rate peak magnitude and contraction strength.     

Inhibition of pericranial muscle activity, respiration, and heart rate enhances auditory sensitivity

We investigated whether previously observed inhibition of pericranial electromyographic (EMG) activity, respiration, and heart rate during sensory intake processes improves auditory sensitivity. Participants had to detect weak auditory stimuli. We found that EMG activity in masticatory and lower facial muscles, respiration, and heart rate were more strongly inhibited when stimulus intensity was gradually lowered to threshold level whereas EMG of upper facial muscles progressively increased. Detection of near-threshold stimuli was inversely related to prestimulus EMG levels in masticatory and lower facial muscles. In two additional experiments, it was investigated whether steady, voluntary contractions negatively influence auditory sensitivity. As expected, contraction of zygomaticus produced an increase in auditory threshold in comparison with contraction of corrugator or first dorsal interosseus. It is concluded that attention to external stimuli is accompanied by quieting of those somatic activities that produce internal noise or are accompanied by impaired middle ear transmission of auditory stimuli.     

颈椎牵引过程中颈部肌电信号变化规律与力学特点

目的观察颈椎牵引在不同加载质量和牵引角度时颈部肌肉表面肌电(electromyography,EMG)信号的变化特点,并与Any Body软件颈椎建模仿真所得的相关肌肉力活性变化特点进行对比,验证仿真结果的合理性。方法选取10例青年志愿者,行仰卧位颈椎牵引,JE-TB0810表面肌电仪测试颈部双侧胸锁乳突肌、斜方肌上部EMG信号,利用平均肌电值(average EMG,AEMG)和平均功率频率(mean power frequency,MPF)分析颈部EMG信号的变化规律。结果斜方肌上部和胸锁乳突肌AEMG均随着加载质量和牵引角度的增大而增大,差异均具有统计学意义(P0.05),斜方肌上部AEMG较胸锁乳突肌高,差异有统计学意义(P0.05);2对肌肉在不同牵引角度和加载质量下MPF比较,差异无统计学意义(P0.05);实验结果与颈椎牵引建模仿真所得斜方肌上部和胸锁乳突肌肌肉力活性特点相符。结论仿真结果具有一定的合理性,临床上可根据颈部肌肉的兴奋程度和疲劳时间合理施加牵引重量,既达到治疗效果,也提高患者的舒适性,为颈椎牵引设备的进一步研制和改进提供重要参考。     

Consequences of prolonged total body immersion in cold water on muscle performance and EMG activity

The consequences of a prolonged total body immersion in cold water on the muscle function have not been documented yet, and they are the object of this French Navy research program. Ten elite divers were totally immerged and stayed immobile during 6 h in cold (18 and 10°C) water. We measured the maximal voluntary leg extension (maximal voluntary contraction, MVC) and evoked compound muscle potential (M wave) in vastus lateralis and soleus muscles at rest, after a submaximal (60% MVC) isometric extension allowing the measurement of the endurance time (Tlim). The power spectrum of surface electromyograms (EMG) was computed during 60% MVCs. MVCs and 60% MVC maneuvers were repeated four times during the immersion. Data were compared with those obtained in a control group studied in dry air condition during a 6-h session. Total body cooling did not affect MVC nor Tlim. The M wave duration increased in the coolest muscle (soleus), but only at 10°C at rest. There were no further fatigue-induced M wave alterations in both muscles. During 60% the MVCs, a time-dependant increase in the leftward shift of the EMG spectrum occurred at the two temperatures. These EMG changes were absent in the control group of subjects studied in dry air. The plasma lactate concentration was elevated throughout the 18 and mostly the 10°C immersion conditions. Throughout the 18°C immersion study, the resting potassium level did not significantly vary, whereas at 10°C, a significant potassium increase occurred soon and persisted throughout the study. Thus, total body immersion in cold water did not affect the global contractile properties of leg muscles during static efforts but elicited significant alterations in electromyographic events which may be related to the variations of interstitial fluid composition.     

Simultaneous measurement of surface EMG and movements for clinical use

A system for simultaneous measurement of surface EMG, joint movement and temporal parameters of gait has been developed for clinical use. Some design constraints, imposed by the clinical situation, are indicated. Multiple cycles of movement are recorded and averaged patterns of muscle activation and joint movements are determined. Data processing runs concurrently with data acquisition, so that the results are available for clinical interpretation immediately after the measurement. Instrumentation, signal processing and software are described and some examples of application of the system for evaluation of therapies and functional aids are presented. It is proposed that clinically relevant quantitative information can be obtained by comparison of different recordings of the individual patient rather than comparison with patterns found with normal subjects.     

Validation of surface EMG as a measure of intravaginal and intra-abdominal activity: Implications for biofeedback-assisted Kegel exercises

This study validates surface EMG as a measure of pelvic muscle and abdominal activity by showing its high correlation to internal pressure data. Using standardized scores, between-subjects correlation of perineal EMG and intravaginal pressure was r= .75, and the correlation of abdominal EMG and intra-abdominal pressure was r= .72. Discriminant validity was also demonstrated by showing low correlation between standardized abdominal and perineal EMG measurements (r= .10). A repeated measures multivariate analysis of variance demonstrated that visual and auditory biofeedback of EMG during pelvic floor contractions increases intravaginal pressure when compared with trials without biofeedback. Potential benefits of fabric electrodes include reduced invasiveness and risk and the ease with which patients can utilize this technology for home practice.     

The joint effect of mood, task valence, and task difficulty on effort-related cardiovascular response and facial EMG

This study investigated whether a pleasant task with high potential for mood regulation could eliminate the motivational deficit of people facing a difficult task in a negative mood. Cardiovascular and facial EMG reactivity of 88 University students were measured during habituation, mood inductions, and an either pleasant or unpleasant scenario completion task that was either easy or difficult. In the unpleasant condition cardiovascular reactivity was modest, particularly in the negative-mood/difficult condition. But when the task was pleasant, cardiovascular reactivity in the negative-mood/difficult condition was stronger than in all other conditions, reflecting the elimination of the motivational deficit. Moreover, facial EMG reactivity indicated efficient mood manipulations. In summary, the findings are interpreted as further support for the mood-behavior-model [Gendolla, G.H.E., 2000. On the impact of mood on behavior: an integrative theory and a review. Rev. Gen. Psychol. 4, 378–408].